1. Field of the Invention
The present invention relates touch sensitive control panels of the kind comprising a front plate preferably of a dielectric material such as glass, and electrodes disposed on a reverse side thereof together with electronic circuits where the front plate carries markings that indicate touch areas so that touching by a finger completes an operative coupling to respective electrodes disposed on the reverse side so that the panel unit provides selective control signals from the electronic circuits.
2. Description of the Prior Art
Such control panels are increasingly used in various kinds of electrical and electronic equipment because they may advantageously replace panels with mechanical switches or rotary or pushbutton activated elements. A light touch upon a selected area controls the desired function such as a starting or stopping or an increasing or decreasing control function without use of mechanically completed switching action. Normally the aforementioned type of control panel functions by a capacitive coupling.
In particular because this kind of control panel is known it is not necessary to discuss the general advantages of their use in detail here. Control panels are predominantly manufactured by specialty manufacturers because their manufacture is not performed by mounting of ready-made special switches and controllers and requires the manufacture of both the panel plate and at least the necessary electronic circuitry.
It has, however, been possible to prepare an intermediate stage where the manufacture of the panel plate itself is a specialized task but the electronic circuitry may be placed on a conventional printed circuit board prepared with suitable contacts for establishing contact with specific electrode areas on the reverse side of the front plate. These defined areas are typically made as a coating of graphite powder which has been fixed reliably to the reverse side of the front plate so that the electrode areas are located at a well-defined position and are easily accessible for establishing contact with projecting contact elements on the printed circuit board since these elements require only that the coatings abut the contact elements in an uncritical fashion.
However considerable contact problems still exist because mechanical fitting of the relevant contact parts is used. Contamination may make the establishment of an effective connection difficult.